1. Field of the Invention
The present invention relates generally to High-Definition Multimedia Interface systems.
2. Description of the Related Art
High-Definition Multimedia Interface (HDMI) is a compact audio-video connector interface directed to transmittal of uncompressed digital data streams. On a single cable, HDMI supports television (TV) and personal computer (PC) video formats including standard, enhanced and high-definition video along with up to 8 channels of digital audio. Development of HDMI 1.0 began in early 2002 under direction of the HDMI founders (Hitachi, Matsushita Electric Industrial (Panasonic), Phillips, Silicon Image, Sony, Thomson (RCA), and Toshiba). The HDMI specification has been adopted by over 800 consumer electronics (CE) and PC companies and HDMI products generally began shipping in autumn of 2003.
HDMI devices are manufactured to adhere to various specification versions in which each version has an assigned number such as 1.0, 1.2, or 1.3a. The HDMI 1.3 specification defines category 1 cables which have been tested at a pixel clock rate of 74.5 MHz and category 2 cables which have been tested at a pixel clock rate of 340 MHz to meet a set of required parameter specifications (inter-pair skew, far-end crosstalk, attenuation, differential impedance) or, alternatively, to meet non-equalized/equalized eye diagram requirements. HDMI cables that are manufactured with lower-quality construction and materials can generally meet the HDMI performance requirements at distances up to something on the order of 5 meters whereas higher-quality cables can generally meet the requirements at distances up to something on the order of 15 meters.
Currently, there are three HDMI connector types. The type A connector has outer dimensions of 4.45×13.9 millimeters and provides 19 pins with bandwidth to support current high-definition television (HDTV) modes. The type B connector has outer dimensions of 4.45×21.2 millimeters and provides 29 pins to double the bandwidth of type A to thereby support future high-resolution displays. A type C mini-connector is also provided to support mobile devices.
HDMI facilitates exchange of video, audio and auxiliary data in three modes called the Video Data Period, the Data Island Period and the Control Period. Pixels of an active video line are transmitted during the Video Data Period. During the Data Island Period (which occurs during horizontal and vertical blanking intervals), audio and auxiliary data pixels are transmitted. The Control Period is positioned between these two periods.
One objective of the HDMI protocol is to reduce several conventional cables that traditionally interconnect a digital source (i.e., a source of digital video and/or audio signals) and a digital sink (i.e., a device that responds to the digital video and/or audio signals) down to a single cable. HDMI was developed for consumer electronics products and it thus contrasts with an earlier protocol digital video interface (DVI) that was developed for use by computers. DVI also provides digital connection between sources and sinks but it doesn't carry audio signals which implies that an extra cable is required for an audio connection. HDMI, however, is fully backward compatible with DVI so that that only a DVI-to-HDMI cable adaptor is required for use with a DVI system. This opens HDMI to a wide range of DVI-equipped products from a variety of manufacturers. In contrast to DVI, HDMI facilitates higher resolutions, connects both video and audio signals, supports two-way communication between source and sink, and its connectors are significantly smaller.
Similar to DVI, HDMI transports data via the transition minimized differential signaling (TMDS) encoding protocol. TMDS conveys data by transitioning between ‘1’ and ‘0’ states while, at the same time, minimizing the state transitions. Reducing the state transitions substantially reduces electromagnetic interference (EMI) levels on the HDMI cable. In addition, however, TMDS acts to minimize long strings of identical states which otherwise can cause detection errors. In this process, incoming 8-bit data is encoded into a 10-bit transition-minimized, DC-balanced word. Three TMDS data channels (CH0, CH1 and CH2) are provided in an HDMI cable with each channel consisting of a signal conductor, an inverse signal conductor, and a ground conductor. A fourth channel (also comprising signal conductor, inverse signal conductor and ground) is dedicated to carry a TMDS clock signal.
Another cable conductor is dedicated to consumer electronic control (CEC) which allows a system user to command and control multiple CEC-enabled devices with one remote control and for individual CEC-enabled devices to command and control each other without user intervention. CEC has the capability of turning all remote controls in a system into universal remotes so that, for example, a single button can switch on all devices that are needed to play back content. In an exemplary scenario, a DVD player could turn on a sink device and associated surround sound systems that are needed for playback.
Other cable conductors are directed to display data channel (DDC) which allows a source device (e.g., a DVD player) to determine the audio and visual capabilities of a sink device. A DDC query from the source device prompts the display to respond with associated display and interface information (e.g., manufacturer name, model number, acceptable data formats, and other display capabilities. DDC can, for example, automatically manage a display device so that a consumer need not alter settings to obtain the highest quality output. DDC is realized with a data conductor (SDA) and a clock conductor (SCL). A ground for both CEC and DDC is carried on a separate conductor. After successful completion of these DDC communications, the sink device can be enabled to receive clock and TMDS signals from the source device.
In order to facilitate DDC communications, another cable connector, called hot plug direct (HPD), permits the source device to detect when a sink device has been connected to it. When an HDMI cable is mounted to the sink device, this device detects that the source device is providing +5 V on the +5V conductor. In response, the sink device places a high level voltage on the HPD conductor. When the source device detects this signal on its HPD conductor, it then inaugurates the DDC communication.